The present invention relates generally to a rotating electrical machine employing a superconductive coil. More particularly, the present invention relates to a multilayer radiation shield for insulating a superconductive rotor coil for a rotating electrical machine.
Rotating electrical machines, such as motors and generators, have a rotor and a stator that are magnetically coupled. Typically, the rotor has a coil that is used to produce a magnetic field. Electricity flowing through the rotor coil produces the magnetic field. In a generator, the rotor is coupled to a prime mover that rotates the rotor, producing a rotating magnetic field that induces a voltage in the stator. The voltage produced in the stator may be used to supply power to an electrical grid. In a motor, the stator produces a rotating magnetic field that interacts with the magnetic field produced by the rotor coil to induce rotation of the rotor.
Conventional copper conductors are commonly used to form the rotor coils. However, the electrical resistance of copper is sufficient to produce a substantial amount of resistive heat losses in the rotor coil, which reduces the efficiency of the rotating machine. In response to the losses caused by conventional copper conductors, superconductors have been developed for use as rotor coils. A superconductor is a material that loses its electrical resistance below a characteristic transition temperature, making it desirable for use as a rotor coil.
In rotating machines employing a superconductive rotor coil, the rotor coil is cooled by a cryogenic fluid to lower the temperature of the superconductive coil below the transition temperature. Below the transition temperature, the superconductive rotor coil enters a superconducting state and loses its electrical resistance. Typically, a cryogenic fluid is provided to the superconductive coil by an external source of cryogenic fluid. The cryogenic fluid absorbs heat from the superconductive rotor coil, which maintains the rotor coil below the transition temperature and in a superconducting state. An insulating material may also be applied between the superconductive coil and the rotor body and surrounding structure. Such insulating material may be a multi-layer insulation application. A low conductivity spacer may be provided between the insulation layers to maintain separation of the multiple layers.
However, a number of problems are associated with providing a low conductivity physical spacer to maintain a separation between successive layers of insulating sheets of a multi-layer insulation application. Most notably, conventional multi-layer insulation applications will crush under centripetal loads present in rotating electrical machines, rendering the conventional multi-layer insulation application ineffective.
There is a need, therefore, for an improved technique for insulating a superconductive rotor coil for a rotating electrical machine. There is a particular need for a multilayer technique, which can be employed to insulate a superconductive rotor coils that does not crush under centripetal loads present in rotating machines.